I’ve often wondered how well fertigating plants simply by mixing soil and water well regularly would perform…

You are after all helping to dissolve soil nutrients into the water for soluble nutrient loving plant roots to take up.

Notice how much soil disturbance this subsoil watering wand creates. The murky water is effectively fertigating the plant and aerating the soil all in one action.

That’s great right?

A while ago, before I knew better, I came up with the idea of using an ultrasonic cleaner filled with water and soil to fertigate with. You ultrasonically shake the soil to bits to dissolve the nutrients and then water it on. Part of me still wants to perform that experiment…

However I have a few concerns with any soil disturbance method. The first includes the break down of organic structure of the soils. You can see clods forming large aggregates on the surface of bare soil in the wand video. This tends to happen in soil deficient in organic matter and also calcium as it leaches away and the clay particles bind to one another. Sulfur and boron among others tend to leach as well.

By constantly destroying the soil structure you destroy microbe homes and the microbial exudates that hold soil particles together. Small colloids that become suspended in the water either then end up together or at the top of the soil and will often create a soil crust or large clods when they dry out. Take a look at the classic jam jar soil shake test below and see what I mean. Up top you have organic matter floating, followed by clay, silt and sand particles at the bottom. That organic matter dries in the sun above a layer of clay and ends up oxidising away into the atmosphere, or if you’re lucky becomes food for the subsurface microbial survivors in that clay. The clay then forms a barrier, water won’t penetrate and instead runs off or sits on the surface and then evaporates.

Heavy rain can also create a similar problem in dispersive soils with mineral imbalances.

Notice how dry the top soil was. It has no structure, no organic matter, it will hold little water. That’s unproductive soil. The most valuable soil, the layer at the edge between air and soil with the most aeration, is going to waste.